Radio frequency regulation is covered in Section V. (Articles 32-57) of the Electronic Communications Act (31 May 2004). (The link in that last sentence is to the Government's unofficial English translation of the law; click here for the law in Slovenian.) Article 35 paragraph (3) authorizes the use of radio frequencies without a specific assignment decision by the regulator, so long as the regulator has defined a method for unassigned use of that part of the spectrum.
"Splošni akt o načrtu uporabe radijskih frekvenc" (General act on radio frequency utilization plan), Agency for Post and Electronic Communication (APEK), February 2006, 157 pages in side-by-side Slovenian and English translation. Includes a comprehensively annotated table of frequency allocations that replaces the 2002 version. Here is a link to the version published in the 31 January 2006 edition of Slovenia's official gazette (Uradni list), without the English translation.
NeoWLAN - Slovene public access wireless network - includes a list of dozens of free hotspots.